Thin film deposition techniques are widely used in the manufacturing of microfeatures to form a coating on a workpiece that closely conforms to the surface topography. The size of the individual components in the workpiece is constantly decreasing, and the number of layers in the workpiece is increasing. As a result, both the density of components and the aspect ratios of depressions (i.e., the ratio of the depth to the size of the opening) are increasing. Thin film deposition techniques accordingly strive to produce highly uniform conformal layers that cover the sidewalls, bottoms, and corners in deep depressions that have very small openings.
One widely used thin film deposition technique is Chemical Vapor Deposition (CVD). In a CVD system, one or more precursors capable of reacting to form a solid thin film are mixed while in a gaseous or vaporous state, and then the precursor mixture is presented to the surface of the workpiece. The surface of the workpiece catalyzes the reaction between the precursors to form a solid thin film at the workpiece surface. A common way to catalyze the reaction at the surface of the workpiece is to heat the workpiece to a temperature that causes the reaction.
Although CVD techniques are useful in many applications, they also have several drawbacks. For example, if the precursors are not highly reactive, then a high workpiece temperature is needed to achieve a reasonable deposition rate. Such high temperatures are not typically desirable because heating the workpiece can be detrimental to the structures and other materials already formed on the workpiece. Implanted or doped materials, for example, can migrate within the silicon substrate at higher temperatures. On the other hand, if more reactive precursors are used so that the workpiece temperature can be lower, then reactions may occur prematurely in the gas phase before reaching the substrate. This is undesirable because the film quality and uniformity may suffer, and also because it limits the types of precursors that can be used.
Atomic Layer Deposition (ALD) is another thin film deposition technique. FIGS. 1A and 1B schematically illustrate the basic operation of ALD processes. Referring to FIG. 1A, a layer of gas molecules A coats the surface of a workpiece W. The layer of A molecules is formed by exposing the workpiece W to a precursor gas containing A molecules and then purging the chamber with a purge gas to remove excess A molecules. This process can form a monolayer of A molecules on the surface of the workpiece W because the A molecules at the surface are held in place during the purge cycle by physical adsorption forces at moderate temperatures or chemisorption forces at higher temperatures. Referring to FIG. 1B, the layer of A molecules is then exposed to another precursor gas containing B molecules. The A molecules react with the B molecules to form an extremely thin layer of solid material on the workpiece W. The chamber is then purged again with a purge gas to remove excess B molecules.
FIG. 2 illustrates the stages of one cycle for forming a thin solid layer using ALD techniques. A typical cycle includes (a) exposing the workpiece to the first precursor A, (b) purging excess A molecules, (c) exposing the workpiece to the second precursor B, and then (d) purging excess B molecules. In actual processing, several cycles are repeated to build a thin film on a workpiece having the desired thickness. For example, each cycle may form a layer having a thickness of approximately 0.5-1.0 Å, and thus several cycles are required to form a solid layer having a thickness of approximately 60 Å.
One drawback of ALD processing is that it has a relatively low throughput compared to CVD techniques. For example, each A-purge-B-purge cycle can take several seconds. This results in a total process time of several minutes to form a single thin layer of only 60 Å. In contrast to ALD processing, CVD techniques require only about one minute to form a 60 Å thick layer. The low throughput limits the utility of the ALD technology in its current state because ALD may create a bottleneck in the overall manufacturing process.
FIG. 3 schematically illustrates a single-wafer CVD/ALD reactor 10 having a reaction chamber 20 coupled to a gas supply 30 and a vacuum pump 40. The reactor 10 also includes a gas dispenser 60 and a heater 50 for supporting the workpiece W in the reaction chamber 20. The gas dispenser 60 includes a plenum 62 operably coupled to the gas supply 30 and a distributor plate 64 having a plurality of holes 66. In operation, the heater 50 heats the workpiece W to a desired temperature, and the gas supply 30 selectively injects the precursors as described above. The vacuum pump 40 maintains a negative pressure in the reaction chamber 20 to draw the gases from the gas dispenser 60 across the workpiece W and then through an outlet of the chamber 20.
In photoselective CVD processing, the reaction chamber 20 may further include a laser 70 configured to generate a laser beam 72 for activating at least one of the precursors. The laser 70 produces the laser beam 72 along a beam path generally parallel to the workpiece W, with the laser beam 72 positioned between the gas dispenser 60 and the workpiece W to selectively activate a precursor(s) before the precursor(s) is deposited onto the workpiece W. The activated precursor(s) subsequently reacts with other precursors on the surface of the workpiece W to form a solid thin film.
In addition to CVD and ALD processing, other processing steps are necessary to form features and devices on workpieces. For example, conventional processing includes patterning a design onto a workpiece, etching unnecessary material from the workpiece, depositing selected material onto the workpiece, and planarizing the surface of the workpiece. These additional processing steps are expensive and time-consuming. Accordingly, a need exists to improve the efficiency with which features are formed on workpieces.